1,780 research outputs found
High-order harmonic generation from Rydberg states at fixed Keldysh parameter
Because the commonly adopted viewpoint that the Keldysh parameter
determines the dynamical regime in strong field physics has long been
demonstrated to be misleading, one can ask what happens as relevant physical
parameters, such as laser intensity and frequency, are varied while is
kept fixed. We present results from our one- and fully three-dimensional
quantum simulations of high-order harmonic generation (HHG) from various bound
states of hydrogen with up to 40, where the laser intensities and the
frequencies are scaled from those for in order to maintain a fixed
Keldysh parameter for all . We find that as we increase
while keeping fixed, the position of the cut-off scales in well
defined manner. Moreover, a secondary plateau forms with a new cut-off,
splitting the HHG plateau into two regions. First of these sub-plateaus is
composed of lower harmonics, and has a higher yield than the second one. The
latter extends up to the semiclassical cut-off. We find that this
structure is universal, and the HHG spectra look the same for all
when plotted as a function of the scaled harmonic order. We investigate the
-, - and momentum distributions to elucidate the physical mechanism
leading to this universal structure
Phase-dependent interference fringes in the wavelength scaling of harmonic efficiency
We describe phase-dependent wavelength scaling of high-order harmonic
generation efficiency driven by ultra-short laser fields in the mid-infrared.
We employ both numerical solution of the time-dependent Schr\"{o}dinger
equation and the Strong Field Approximation to analyze the fine-scale
oscillations in the harmonic yield in the context of channel-closing effects.
We show, by varying the carrier-envelope phase, that the amplitude of these
oscillations depend strongly on the number of returning electron trajectories.
Furthermore, the peak positions of the oscillations vary significantly as a
function of the carrier-envelope phase. Owing to its practical applications, we
also study the wavelength dependence of harmonic yield in the "single-cycle"
limit, and observe a smooth variation in the wavelength scaling originating
from the vanishing fine-scale oscillations.Comment: 5 pages, 4 figure
Rabi flopping between ground and Rydberg states with dipole-dipole atomic interactions
We demonstrate Rabi flopping of small numbers of atoms between
ground and Rydberg states with . Coherent population oscillations are
observed for single atom flopping, while the presence of two or more atoms
decoheres the oscillations. We show that these observations are consistent with
van der Waals interactions of Rydberg atoms.Comment: 4 pages, 6 figure
Genistein-induced mir-23b expression inhibits the growth of breast cancer cells
Aim of the study: Genistein, an isoflavonoid, plays roles in the inhibition of protein tyrosine kinase phosphorylation, induction of apoptosis, and cell differentiation in breast cancer. This study aims to induce cellular stress by exposing genistein to determine alterations of miRNA expression profiles in MCF-7 cells. Material and methods: XTT assay and trypan blue dye exclusion assays were performed to examine the cytotoxic effects of genistein treatment. Expressions of miRNAs were quantified using Real-Time Online RT-PCR. Results: The IC50 dose of genistein was 175 μM in MCF-7 cell, line and the cytotoxic effect of genistein was detected after 48 hours. miR-23b was found to be up-regulated 56.69 fold following the treatment of genistein. It was found that miR-23b was up-regulated for MCF-7 breast cancer cells after genistein treatment. Conclusions: Up-regulated ex-expression of miR-23b might be a putative biomarker for use in the therapy of breast cancer patients. miR-23b up-regulation might be important in terms of response to genistein. © 2015, Termedia Publishing House Ltd. All rights reserved
Spiking neural network model of reinforcement learning in the honeybee implemented on the GPU
No description supplie
Fast Ground State Manipulation of Neutral Atoms in Microscopic Optical Traps
We demonstrate Rabi flopping at MHz rates between ground hyperfine states of
neutral Rb atoms that are trapped in two micron sized optical traps.
Using tightly focused laser beams we demonstrate high fidelity, site specific
Rabi rotations with crosstalk on neighboring sites separated by at
the level of . Ramsey spectroscopy is used to measure a dephasing time
of which is 5000 times longer than the time for a
pulse.Comment: 4 pages, 4 figure
Refractive Index Enhancement with Vanishing Absorption in an Atomic Vapor
We report a proof-of-principle experiment where the refractive index of an
atomic vapor is enhanced while maintaining vanishing absorption of the beam.
The key idea is to drive alkali atoms in a vapor with appropriate control
lasers and induce a gain resonance and an absorption resonance for a probe beam
in a two-photon Raman configuration. The strength and the position of these two
resonances can be manipulated by changing the parameters of the control lasers.
By using the interference between these two resonances, we obtain an enhanced
refractive index without an increase in the absorption.Comment: 11 pages, 4 figure
Fundamental open questions on engineering of "super" hydrogen sorption in graphite nanofibers: relevance for clean energy applications
Herein, some fundamental open questions on engineering of “super” hydrogen sorption (storage) in carbonaceous nanomaterials are considered, namely: 1) on thermodynamic stability and related characteristics of some hydrogenated graphene layers nanostructures: relevance to the hydrogen storage problem; 2) determination of thermodynamic characteristics of graphene hydrides; 3) a treatment and interpretation of some recent STM, STS, HREELS/LEED, PES, ARPS and Raman spectroscopy data on hydrogensorbtion with epitaxial graphenes; 4) on the physics of intercalation of hydrogen into surface graphene-like nanoblisters in pyrolytic graphite and epitaxial graphenes; 5) on the physics of the elastic and plastic deformation of graphene walls in hydrogenated graphite nanofibers; 6) on the physics of engineering of “super” hydrogen sorption (storage) in carbonaceous nanomaterials, in the light of analysis of the Rodriguez-Baker extraordinary data and some others. These fundamental open questions may be solved within several years
Nanoscale addressing and manipulation of neutral atoms using electromagnetically induced transparency
We propose to integrate dark-state based localization techniques into a
neutral atom quantum computing architecture and numerically investigate two
specific schemes. The first scheme implements state-selective projective
measurement by scattering photons from a specific qubit with very little cross
talk on the other atoms in the ensemble. The second scheme performs a
single-qubit phase gate on the target atom with an incoherent spontaneous
emission probability as low as 0.01. Our numerical simulations in rubidium (Rb)
atoms show that for both of these schemes a spatial resolution at the level of
tens of nanometers using near-infrared light can be achieved with
experimentally realistic parameters
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